1. Field of the Invention
The present invention relates to a ceramic condenser module which is used in circuits which pass a relatively large amount of electrical current and which is used, for example, for smoothing or snubber purposes at, for example, a high-frequency region, and, more particularly, to a ceramic condenser module having an improved heat-dissipation structure.
2. Description of the Related Art
Various ceramic condenser modules having a plurality of multi-layered ceramic condensers connected in parallel as condensers for use with a large amount of electrical current have been proposed. Such types of ceramic condenser modules, disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 10-241989 and 10-223473, have a plurality of ceramic condensers that are stacked in accordance with the direction of an external electrode in order to form an integral structure. A metallic terminal is joined to this integrally formed structure for achieving electrical connection to an external element.
A single multi-layered ceramic condenser for use with external current is also known.
Multi-layered ceramic condensers for use with a large amount of current generate a relatively large amount of heat. Therefore, it is necessary to efficiently dissipate the heat that is generated therein.
The heat that has been generated by the single multi-layered ceramic condenser mounted onto a substrate is discharged by conduction of heat to the substrate or by convection of heat into the air from an exposed surface of the multi-layered ceramic condenser. In such a structure having a single multi-layered ceramic condenser mounted to a substrate, the natural convection heat transfer coefficient is usually of the order of 0.96. In order to increase the cooling efficiency to a higher value than this, it is necessary to mount, for example, a cooling fin on each condenser.
However, when the single multi-layered ceramic condenser is used, it is directly mounted to a circuit board, so that it is difficult to further increase the heat-dissipation area. In addition, interference with other elements occurs, so that it is difficult to cause the single multi-layered ceramic condenser to contact a cooling member such as a heat sink.
When a conventional ceramic condenser module having a plurality of ceramic condensers that are stacked is used, and is mounted to a circuit board, there are only a heat-dissipation path through which heat is transferred to the substrate through an external electrode and a metallic terminal, and a heat-dissipation path through which heat is discharged by convection of heat from barely exposed side surfaces of the multi-layered ceramic condensers. In other words, since the plurality of ceramic condensers are stacked, heat tends to be confined at the stacked portions of the multi-layered ceramic condensers, so that heat-dissipation efficiency is not satisfactory, thereby resulting in a temperature increase in the ceramic condenser module.
The temperature of a condenser when a load is applied depends upon the heat-dissipation efficiency. Therefore, in a ceramic condenser module having a temperature that tends to reach a high value, it is not possible to make use of the maximum current capacity characteristic of each of the multi-layered ceramic condensers of the condenser module.
When using a large amount of electrical current, in order to increase cooling efficiency, the use of a method using a cooling member, such as a heat sink, may be considered. However, in a conventional ceramic condenser module, the heat sink can easily be in contact with only some of the multi-layered ceramic condensers. Therefore, it is difficult to sufficiently cool the condensers that are located spaced away from the heat sink.
Consequently, in order for a large amount of electrical current to be used in a conventional stacked type ceramic module, it is necessary to increase the capacity by further connecting the plurality of ceramic condenser modules in parallel, thereby increasing the volumes of the condensers and related manufacturing costs.
In order to overcome the problems described above, preferred embodiments of the present invention provide a ceramic condenser module that has greatly increased heat dissipation efficiency and, thus, provides a desired current capacity, and which has a greatly reduced size.
According to a preferred embodiment of the present invention, a ceramic condenser module includes at least one multi-layered ceramic condenser and a substrate arranged such that the at least one multi-layered ceramic condenser is mounted in close contact therewith, the substrate including a plurality of electrode lands electrically connected to the at least one multi-layered ceramic condenser. In the ceramic condenser module, a total surface area S1, which is equal to the total of the surface areas of the at least one multi-layered ceramic condenser and the substrate, is equal to or greater than about 1.3 times a total surface area S2, which is equal to the total area of an outer surface of the at least one stacked type ceramic mounted to the substrate excluding a surface thereof opposing the substrate.
In a first modification of the first preferred embodiment of the present invention, the at least one multi-layered ceramic condenser is adhered to the substrate preferably via resin containing a metal oxide.
When the structure of the first preferred embodiment or the first modification thereof is used, there may be realized a second modification thereof in which a plurality of multi-layered ceramic condensers are mounted to the substrate without being stacked upon each other, the plurality of multi-layered ceramic condensers being electrically connected in parallel via the plurality of electrode lands.
When any one of the structures of the first preferred embodiment and the first and second modifications thereof is used, there may be realized a third modification in which the plurality of multi-layered ceramic condensers are mounted to a front surface and a back surface of the substrate.
When any one of the structures of the first preferred embodiment and the first, second and third modifications thereof is used, there may be realized a fourth modification in which the at least one multi-layered ceramic condenser or the plurality of multi-layered ceramic condensers and the substrate are electrically connected using a metallic terminal.
When any one of the structures of the first preferred embodiment and the first through fourth modifications thereof is used, there may be realized a fifth modification in which the substrate includes a terminal electrode for electrical connection to an external portion, a through hole for securing the ceramic condenser module with a screw or bolt, or other suitable fastening element, being disposed in a portion where the terminal electrode is provided.
When any one of the structures of the first preferred embodiment and the first through fifth modifications thereof is used, there may be realized a sixth modification in which the substrate includes a terminal electrode for electrical connection to an external element, and a metallic terminal is joined to the terminal electrode.
When any one of the structures of the first preferred embodiment and the first through sixth modifications thereof is used, there may be realized a seventh modification in which a through hole electrode for electrically connecting an electrode on each of the front surface and the back surface of the substrate is disposed in the substrate.
According to another preferred embodiment of the present invention, a power converter includes at least one ceramic condenser module constructed according to any one of the first preferred embodiment and the first through seventh modifications thereof.